Technical Field
The present invention relates to a power conversion device which can supply a stable voltage to a load even when the voltage of an alternating current power source drops.
Background Art
As a power conversion device which can supply a stable voltage to a load even when the voltage of an alternating current power source drops, an on-line type power conversion device is known. FIG. 7 is a diagram for illustrating the on-line type power conversion device disclosed in Japanese Patent Application Publication No. 10-075581 and International Publication No. WO2012/067167A1. In the drawing, 1 is a single-phase alternating current power source, 2 is a capacitor, 3 is a converter, 4 is an inverter, 5 is a filter, and 6 is a load.
The power conversion device converts the voltage of the alternating current power source 1 once to a direct current voltage, converts the direct current voltage again to an alternating current voltage, and supplies the alternating current voltage to the load 6.
Herein, the operation of converting the voltage of the alternating current power source 1 to a direct current voltage is carried out by the converter 3. The converter 3, by turning on/off switching elements Qp and Qn, converts the voltage of the alternating current power source 1 to a direct current voltage. The direct current voltage generated by the converter 3 is smoothed by capacitors Cp and Cn. The direct current voltage smoothed by the capacitors Cp and Cn is output to the inverter 4.
The inverter 4, by selectively turning on/off the switching elements Q1 and Q2 and a bidirectional switch BS1, converts the direct current voltage of the capacitors Cp and Cn to an alternating current voltage Vu of a pulse-width controlled pulse train. The filter 5 removes a harmonic component contained in the alternating current voltage Vu of the pulse train, and outputs a sinusoidal alternating current voltage Vload. The sinusoidal alternating current voltage Vload is applied to the load 6.
The heretofore described power conversion device includes, as its operation modes, a direct feed mode, a boost mode, a buck mode, and a backup mode. In which mode the power conversion device operates is determined by detecting the voltage of the alternating current power source 1 or the like.
The direct feed mode is an operation mode in which to output the voltage of the alternating current power source 1 as the alternating current voltage Vload when the voltage of the alternating current power source 1 is within a predetermined range. In this operation mode, the switching elements Q1 and Q2 are turned off, and the bidirectional switch BS1 is turned on.
The boost mode is an operation mode in which to boost the voltage of the alternating current power source 1, and output the alternating current voltage Vload having a predetermined amplitude, when the voltage of the alternating current power source 1 becomes lower than a predetermined value. In this operation mode, the switching elements Q1 and Q2 and the bidirectional switch BS1 are selectively turned on/off based on a pulse-width modulated control signal.
The buck mode is an operation mode in which to buck the voltage of the alternating current power source 1, and output the alternating current voltage Vload having a predetermined amplitude, when the voltage of the alternating current power source 1 becomes higher than the predetermined value. In this operation mode, the switching elements Q1 and Q2 are turned off, and the bidirectional switch BS1 is turned on/off based on a pulse-width modulated control signal.
The backup mode is an operation mode in which to output the alternating current voltage Vload having a predetermined amplitude, using the direct current voltage of the capacitors Cp and Cn, when an interruption of the alternating current power source 1 is detected. In this operation mode, the bidirectional switch BS1 is turned off, and the switching elements Q1 and Q2 are selectively turned on/off based on a pulse-modulated control signal.